[old_tv_nut]

Ground sounds OK.

Not sure what to suggest about the antenna except maybe running it as straight as possible without bending back. When I had a crystal set as a kid in Chicago I threw the antenna wire out the upstairs window and into a tree. It was mostly horizontal and maybe 20 feet long and got a few Chicago stations.

Diode direction should be immaterial, just changes the phase of the audio by 180 degrees.